Perovskite-type compositions containing pentavalent Ru

ABSTRACT

Metal oxides of the formula 
     
         Q.sub.2 MRuO.sub.6 
    
     wherein Q is barium or strontium, and M is yttrium, bismuth or a rare earth metal of atomic number 57 to 70, in which ruthenium has a valence of 5, and which have a perovskite-type crystal structure are highly useful as emission catalysts for NO x  reduction and oxidation of CO.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to metal oxides containing pentavalent rutheniumand having a perovskite-type crystal structure, and to their use asemission control catalysts.

2. Description of the Prior Art

It is known that Ru and Ru-containing compounds are good reductioncatalysts, and thus their use to reduce NO_(x) to N₂ in exhaust gasesfrom internal combustion engines has been proposed. However, Ru isnormally volatile at the high temperatures encountered in these exhaustgases.

In Platinum Metals Review, vol. 18, no. 1, p. 2 (1974), Shelef et al.teach stabilizing Ru against loss by volatilization by incorporating Ruoxide in a compound with basic oxides such as BaRuO₃.

In a dissertation submitted to the University of Connecticut in 1965, P.C. Donohue disclosed hexagonal close packed structures of alkaline earthruthenium oxides of the formula Ba(RuM)O₃ in which M is various metals,some of said compounds having perovskite-type crystal structures andcertain others having ruthenium in the pentavalent state. This subjectis further disclosed by Donohue et al. in Inorganic Chemistry, vol. 5,no. 3, pp. 339-342 (1966). In this article compounds in which M is Zr,Mn, Ni, and Mg are described.

SUMMARY OF THE INVENTION

In accordance with this invention we have discovered metal oxidescontaining pentavalent ruthenium which exhibit perovskite-type crystalstructures and are of the formula

    Q.sub.2 MRuO.sub.6

wherein Q is barium or strontium, and M is yttrium, bismuth or a rareearth metal of atomic number 57 to 70, provided that when Q isstrontium, M is not bismuth. These metal oxides are useful as emissioncontrol catalysts for internal combustion engines. Specific metal oxideswhich exhibit these properties are of the formulae

    Ba.sub.2 M'RuO.sub.6

and

    Sr.sub.2 M"RuO.sub.6

in which M' is yttrium, bismuth or a rare earth metal of atomic number57 to 70 and M" is yttrium or a rare earth metal of atomic number 57 to70.

DETAILED DESCRIPTION OF THE INVENTION

The metal oxides of this invention are pentavalent ruthenium compoundswhich have two basic characteristics, namely, they (1) have aperovskite-type crystal structure and (2) are of the formula

    Q.sub.2 MRuO.sub.6.

specific metal oxides which are suitable include Ba₂ LaRuO₆, Ba₂ GdRuO₆,Ba₂ EuRuO₆, Ba₂ DyRuO₆, Ba₂ CeRuO₆, Ba₂ RuTbO₆, Ba₂ BiRuO₆, Ba₂ YRuO₆,Sr₂ LaRuO₆, Sr₂ NdRuO₆, Sr₂ GdRuO₆, Sr₂ HoRuO₆, Sr₂ LaRuO₆, Sr₂ YbRuO₆and Sr₂ YRuO₆. The most preferred pentavalent ruthenate composition isBa₂ LaRuO₆.

It is known in the art that Ru-containing compounds are good reductioncatalysts, especially for the reaction of NO_(x) to N₂. Compositions,however, containing lower valent ruthenates have a tendency to form Ru°on reduction leading to Ru-loss via RuO₄ volatilization if intermittentoxidizing exposure occurs, thereby drastically reducing theeffectiveness of the catalyst. The advantage of the compound of thisinvention is their greater thermal stability.

The catalytic stability of the compositions of the present invention isreinforced against Ru loss by volatilization under oxidation-reductionconditions by (1) stabilizing the ruthenate compositions with threebasic ions (2 alkaline earth metal + rare earth metal) per Ru incontrast to, e.g. BaRuO₃ where it is stabilized by only one basic ion,and (2) utilizing ruthenium in its inherently more stable pentavlentstate.

The compositions characterizing the present invention, because of theirperovskite-type crystal structures and the pentavalent state of thecombined ruthenium which is stabilized in the presence of three basiccations, exhibit high stability toward reduction, making them highlyuseful as emission catalysts for NO_(x) reduction where x = 1 or 2 andoxidation of CO.

By "perovskite-type crystal structures" is meant crystal structuressimilar to those of perovskite (CaTiO₃). Ideal perovskite structures(ABO₃) contain cations of appropriate relative sizes and coordinationproperties and have cubic crystalline forms in which the corners of theunit cubes are occupied by the larger type A cations (each coordinatedwith twelve oxide ions), the centers of the cubes are occupied by thesmaller type B cations (each coordinated with six oxide ions), and thefaces of the cubes are occupied by oxide ions. Variations anddistortions of this fundamental cubic crystal structure are known amongmaterials commonly considered to be perovskites or perovskite-like.Distortions of the cubic crystal structure of perovskite andperovskite-like metal oxides include rhombohedral, orthorhombic,pseudocubic, tetragonal, and pseudotetragonal modifications. In allthese crystal structures, it is required that the total number of A sitecations should substantially equal the total number of B site cations,also that the combined charge of the cations substantially equals thecharge on the oxygen atoms.

The formation of these structures is a function of the ionic radii andelectronegativity of the ions. Goldschmidt [GeochemischeVerteilungsgesotze der Elementa VII, VIII, (1927,28)] defined thetolerable limits for perovskite formation, t - (r_(a) + r_(x))/∫2(r_(b) + r_(x)) where, in ABX₃, r stands for the radii. Theperovskite-type structure occurs when t is in the ragne of 0.75-1.00.When t is greater than 1.00, distortion to a hexagonal cell structuremay occur. Cubic perovskite require 0.9 < t > 1.0. Between 0.75 <t > 0.9a buckling of the lattice occurs causing distortion. All of the metaloxides of this invention are of a perovskite-type structure.

Complete ranges of solid solutions are possible for all the compositionsfalling within the scope of the present invention with the exception ofthe border-line cases such as Ba₂ YRuO₆, Ba₂ CeRuO₆, Ba₂ TbRuO₆ and Ba₂DyRuO₆ where partial solid solutions may be expected.

Additionally, partial solid solutions with other transition metalperovskite-type structures may be expected e.g. with LaCoO₃. This leadsto greater enhancement of catalytic activity.

Since the perovskite structure is known to exhibit both cation and anionnonstoichiometry as discussed by J. B. Goodenough and J. J. Longo,Landolt-Bornstein, Vol. 4a, 126-314 (1970), the compositions of thepresent invention may also exhibit nonstoichiometry, e.g., in a reducingatmosphere some oxygen may be lost, giving rise to such compositions asBa₂ LaRuO_(6-x) where x is 0 to about 0.1.

The high oxygen analysis of several of the compositions to be describedin the examples to follow is thought to be due to adsorbed CO₂. Theperovskite-type structure cannot easily accommodate excess oxygen (e.g.Ba₂ GdRuO_(6+x)) since there are no lattice sites available. The directvalence analysis described in Example 1 is considered more reliable thanthe oxygen analysis and shows the Ru valence is primarily +5 withpossibly some +4 present.

The compositions of the present invention may be prepared by severalmethods. The most convenient method for study of the isolatedcompositions is to grind and calcine in stoichiometric proportions thecarbonates, nitrates, hydroxide or oxides of the alkaline earth and rareearth ions and Ru powder, nitrate, halide, or oxide. They may also beprepared on supports by impregnation with soluble salts of theconstituents; e.g. their nitrates, followed by drying and calcination.The method of successive impregnation described by M. Shelaf and H. S.Gandi [Platinum Metals Review, 18(1), 2 (1974)] may be used. In thismethod a support is first impregnated with barium nitrate solution andcalcined to convert to the oxide. It is then impregnated with RuCl₃,dried, reduced, and "fixed" by heating in air at 900° C.

As shown in Examples 3 and 6 the ruthenate compositions of the presentinvention show excellent advantage as catalysts for hydrocarbonreduction and especially NO reduction and CO oxidation making themexcellent candidates as emission control catalysts for such applicationsas automotive exhaust gas purification and slack gas NO_(x) abatement.

The compositions of this invention may also be used as semiconductors.For example, Ba₂ EuRuO₆ powder exhibits resistivity at 298k (P_(298k)) =2 × 10³ ohm cm and Ea = 0.1 eV, and Ba₂ BiRuO₆ exhibits P_(298k) = 2 ×10² ohm cm and Ea = 0.15 eV. These compositions may be used in the manyapplications of semiconductors, e.g. resistors, thermoelectrics, etc.

The following examples illustrate the pentavalent ruthenium metal oxidesof this invention, their preparation, and their use as emission controlcatalysts. All temperatures are in degrees Centigrade.

EXAMPLE I Preparation of Ba₂ GdRuO₆

A well ground mixture of 1.973 g BaCO₃ (0.01 moles), 0.906 g Gd₂ O₃(0.005 moles), and 0.665 g RuO₂ (.005 moles) was heated in air at 1100°C. for 1 hour, reground, and reheated at 1000° C. for 24 hours,reground, and reheated at 1000° C. for 48 hours. The X-ray powderpattern showed a cubic cell a = 4.204 ± 0.001 A and a few weak lines ofextraneous phases amounting to about less than 5%. The powder pattern isshown in Table 1. It may be used to identify the cubic perovskitecompounds of this invention.

Oxygen analysis established the formula. Found: 15.37% O. Calculated forBa₂ GdRuO₆ : 15.26% O.

To establish the valence of Ru as +5, analysis was carried out of theCl₂ generated by the reaction of Ru⁺⁵ with HCl following the proceduredescribed by J. D. Struthers and R. Ward in J. Am. Chem. Soc., 59, 1849(1937). In HCl, Ba₂ GdRuO₆ dissolves and Cl₂ is liberated, 1/2 Cl₂ perRu⁺⁵ or: Ru⁺⁵ + Cl⁻ → Ru⁺⁴ + 1/2 Cl₂.

    ______________________________________                                        Results                                                                       Cl Calculated                                                                              Cl Found   Formula Calculated                                    ______________________________________                                        0.008914     0.007517   Ba.sub.2 GdRuO.sub.5.92                               0.009187     0.007855   Ba.sub.2 GdRuO.sub.5.93                               0.005822     0.005142   Ba.sub.2 GdRuO.sub.5.94                               ______________________________________                                    

Since errors in this method tend to give low results (for example, byincomplete removal of Cl₂), coupled with the oxygen analysis the formulamay safely be assigned as Ba₂ GdRuO₆.

The valence of Ru is +5 or slightly lower. In the formula Ba₂ GdRuO₅.93,the valence distribution is Ba₂ GdRu₀.85 Ru₀.15 O₅.93. The valence of Rumay be slightly less than +5 (in this compound it is +4.85) due to Ononstoichiometry.

Since Gd lies in the middle of the rare earth series, the finding withregard to Ru valence of Ba₂ GdRuO₆ should pertain throughout the series.

EXAMPLE 2 Preparation of Sr₂ GdRuO₆

A well ground mixture of 1.4763 g SrCO₃ (0.01 moles), 0.906 g Gd₂ O₃(0.005 moles), 0.665 g RuO₂ (0.005 moles) was treated similar to Example2. The product showed a single phase powder pattern indexable on thebasis of an orthorhombically distorted perovskite-type cell. The celldimensions are a = 5.798 ± 0.001 A, b = 5.820 ± 0.001 A, C = 8.224 ±0.003 A, and the powder pattern is shown in Table 2.

Oxygen analysis of the material is consistent with the formula Sr₂GdRuO₆. Found: 17.98% O. Calculated: 18.12%. Cl analysis as described inExample 1 shows that Ru valence is close to +5, perhaps slightly below.

    ______________________________________                                        Cl Calculated                                                                            Cl Found  Formula       Ru valence                                 ______________________________________                                        0.00867    0.0073    Sr.sub.2 GdRuO.sub.5.93                                                                     +4.85                                       0.010565  0.009837  Sr.sub.2 GdRuO.sub.5.967                                                                    +4.93                                      0.01022    0.00932   Sr.sub.2 GdRuO.sub.5.95                                                                      4.90                                      ______________________________________                                    

The formula is very close to Sr₂ GdRuO₆. There is always thispossibility of some O nonstoichiometry.

                  Table 1                                                         ______________________________________                                        X-Ray Powder Pattern of Ba.sub.2 GdRuO.sub.6                                  Intensity h       k       l     d.sub.obs                                                                              d.sub.calc                           ______________________________________                                        100       1       1       0     2.9760   2.9727                               2         1       1       1     2.4262   2.4272                               26        2       0       0     2.1026   2.1020                               33        2       1       1     1.7157   1.7163                               ______________________________________                                    

                  Table 2                                                         ______________________________________                                        X-Ray Powder Pattern of Sr.sub.2 GdRuO.sub.6                                  Intensity h       k       l     d.sub.obs                                                                              d.sub.calc                           ______________________________________                                        5         0       1       1     4.7573   4.7511)                                        1       0       1              4.7389)                              35        1       1       0     4.1090   4.1078)                                        0       0       2              4.1122)                              5         1       1       1     3.6783   3.6749                               100       1       1       2     2.9067   2.9062)                                        0       2       0              2.9102)                                        2       0       0              2.8991)                              5         0       2       1     2.7436   2.7435)                                        0       0       3              2.7415)                                        2       0       1              2.7342)                              10        1       0       3     2.4791   2.4784)                                        1       2       1              2.4799)                                        0       1       3              2.4801)                                        2       1       1              2.4747)                              5         0       2       2     2.3762   2.3755)                                        2       0       2              2.3694)                              5         1       1       3     2.2775   2.2803                               75        2       2       0     2.0543   2.0539)                                        0       0       4              2.0561)                              5         2       2       1     1.9935   1.9927)                                        2       0       3              1.9919)                                        0       2       3              1.9955)                              5         2       1       3     1.8842   1.8846)                                        1       2       3              1.8869)                                        3       0       1              1.8815)                                        0       3       1              1.8883)                              10        1       3       0     1.8405   1.8399)                                        1       1       4              1.8386)                                        2       2       2              1.8374)                              10        3       1       0     1.8340   1.8342                               10        1       3       1     1.7964   1.7955)                                        3       1       1              1.7903)                              80        2       0       4     1.6778   1.6771)                                        0       2       4              1.6793)                                        1       3       2              1.6794)                              55        3       1       2     1.6730   1.6751                               5         1       3       3     1.5278   1.5277)                                        1       1       5              1.5270)                                        3       1       3              1.5245)                              35        0       4       0     1.4547   1.4551)                                        2       2       4              1.4531)                              35        4       0       0     1.4504   1.4495                               5         0       0       6     1.3705   1.3707)                                        1       3       4              1.3711)                                        0       4       2              1.3717)                                        3       3       0              1.3692)                                        3       1       4              1.3687)                                        4       0       2              1.3671)                              45        3       3       2     1.2989   1.2991)                                        4       2       0              1.2975)                                        1       1       6              1.3002)                                        2       4       0              1.3005)                              5         3       3       3     1.2253   1.2249)                                        3       1       5              1.2246)                              ______________________________________                                    

EXAMPLE 3 (A) Preparation of Ba₂ LaRuO₆

A well ground mixture of 8.4296 g of BaO₂ (2 mole parts, 4.0548 g of La₂O₃ (1/2 mole part) and 2.5156 g of Ru (1 gram atom part) was heated inair at 900° C, followed by regrinding and reheating at 1100° for 20hours. The X-ray powder diffraction pattern of the product showed acubic perovskite-type cell in which a = 4.26 A.

The powder prepared above was slurry coated onto 1 × 1 × 1/16 inchTortex® ceramic honeycomb cylinders to give a 17.2% coating by weight.These cylinders were used to test the powder as an emission controlcatalyst.

(B) Catalytic Activity in the Recution of Nitric Oxide by CarbonMonoxide

A coated Torvex® cylinder was installed in a stainless steel chamberwith a nominal internal diameter of 2.5 cm, height of 2.5 cm, and volumeof 12.3 cc. Nitrogen containing about 2000 parts per million of nitricoxide and about 10,000 parts per million of carbon monoxide was passedthrough the chamber at a nominal hourly space velocity of about 40,000hr.⁻¹ and pressure of 1 psig while the feed gas and the catalyst chamberwere heated in a programmed manner so that the temperature of the gasentering the catalyst chamber increased from about 60° to about 600°over about 90 minutes. Samples of the inlet and exit gases were obtainedperiodically. The nitric oxide in these samples was oxidized to nitrogendioxide and the resulting gas mixture was analyzed by a modification ofthe colorimetric procedure described by B. E. Saltzman in AnalyticalChemistry, Volume 26, pages 1949-1955 (1954). The percent reduction inthe nitric oxide concentration of the gas upon passing through thecatalyst chamber was found to be nil at a catalyst chamber inlettemperature of 100°, 14.3% at 200°, 97.1% at 400°, 98.6% at 500°, and98.6% at 600°. The catalyst temperature was about 660° with the gasentering the catalyst chamber at 600°. From a smooth curve through aplot of these results it was estimated that the conversion of nitricoxide was 25% at about 315°, 50% at about 340°, and 90% at about 390°,and that the "light-off" temperature (the intercept with the temperatureaxis of an extrapolation of the portion of the curve in which the degreeof conversion changed rapidly with temperature) was about 280°. The"light-off" temperature and the temperatures of 25, 50, and 90%conversion after heating the catalyst-coated honeycomb cylinder at about900° for 100 hours were also recorded.

(C) Catalytic Activity in the Oxidation of Carbon Monoxide

The catalytic activity of a coated Torvex® cylinder in the oxidation ofcarbon monoxide was determined in an apparatus and by a proceduresimilar to that described in part (B) above. Nitrogen containing about10,000 parts per million of carbon monoxide and 10,000 parts per millionof oxygen was passed through the catalyst chamber and the entering andexisting gas mixtures were analyzed chromatographically using a columncontaining granules of "Linde" 13X molecular sieve. The conversion ofcarbon monoxide was found to be 6.6% with a catalyst chamber inlettemperature of 140° C, 7.1% at 200°, 5.4% at 245°, and 100% at 275° andat 305°. The temperature of the catalyst was 330° with a catalystchamber inlet temperture of 275°. From a smooth curve through a plot ofthese results it was estimated that the conversion of carbon monoxidewas 25% at about 250°, 50% at about 260°, and 90% at about 270° and thatthe "light-off" temperature was about 245°. The "light-off" temperaturesand the temperatures of 25, 50, and 90% conversion after heating thecatalyst-coated honeycomb cylinder at about 900° for 100 hours were alsorecorded.

The results of the activity tests are as follows:

    ______________________________________                                                      T for conversion of                                             Test     Light-off T                                                                              25%       50%     90%                                     ______________________________________                                        NO + CO  200/200*   230/225*  255/255*                                                                              300/295*                                CO + 1/2 O.sub.2                                                                       205/200*   225/235*  250/250*                                                                              325/275*                                ______________________________________                                         *after 100 hr at 900°.                                            

The results are excellent for NO reduction and in a good range for COoxidation. The high activity after heating shows the superior stabilityof the catalyst.

The stability was further illustrated in thermal gravimetric analysis(TGA) experiments in a simulated emission mixture. In 1% H₂, 4% CO, 95%N₂ at 30 ml/min no weight loss was observed to 900° by TGA. The X-raypowder pattern also showed no change.

TGA in O₂ at 40 ml/min also showed no weight change to 950°.

EXAMPLE 4 Preparation of Ba₂ EuRuO₆

A well ground mixture of 2.9379 g of BaCO₃ (2 mole parts), 1.3098 g ofEu₂ O₃ (1/2 mole part), and 0.7523 g of Ru (1 gram atom part) was heatedin air at 1000°, reground and heated at 1000° for 24 hr. The productshowed a cubic perovskite-type cell a = 4.21 A; calculated cell, a =4.212 A. Oxygen analysis showed that the Ru had a valence of 5. Found:15.53% O, calc'd for Ba₂ EuRuO₆ : 15.39%.

This material was shown to be useful as a reduction catalyst. Thus, 1.5ml of toluene and 1.0 g of NH₃ were heated in a 10-cc shaker tube at450° for 10 min in the presence of about 30.5 g of Ba₂ EuRuO₆. Theproduct contained 11% methyl cyclohexane.

EXAMPLE 5 Preparation of Ba₂ DyRuO₆

A well ground mixture of 2.8925 g of BaCO₃ (2 mole parts), 1.3668 g ofDy₂ O₃ (1/2 mole part), and 0.7407 of Ru (1 gram atom part) was heatedas in Example 4. The product showed a poorly formed perovskite patternand some weak extraneous peaks present. It was reground and heated at1100° for 24 hr. The product was single phase and showed a predominantlycubic perovskite-type cell, a = 4.18 A; calc'd: 4.18 A. Some weakextraneous peaks were still present.

EXAMPLE 6 Preparation of Ba₂ CeRuO₆

A well ground mixture of 2.6135 of BaO₂ (2 mole parts), 0.7800 g of Ru(1 gram atom part) and 1.6063 g of Ce(OH)₄ (1 mole part) was heated at1000° for 1 hr, reground, and heated at 1150° for 4 hr. The X-ray powderpattern was not single phase, so the product was reground and heated at1150° for 48 hr, reground, and reheated at 1250° for 24 hr. The productwas single phase and the X-ray powder pattern showed a distortedperovskite-type cell and weaker peaks of extraneous phases. Oxygenanalysis: Found: 16.62% O; calc'd for Ba₂ RuCeO₆, 15.68%; Ba₂ RuCeO₆.5,16.77%; Ba₂ Ru₀.8 CeO₆, 16.22%. The higher percent O may indicate thatRu is +6 or Ce is +4 and cation vacancies are present.

EXAMPLE 7 Preparation of Ba₂ TbRuO₆

A well ground mixture of 2.7023 g of BaO₂ (2 mole parts), 1.4915 g ofTb₄ O₇ (1/4 mole part), and 0.8064 g of Ru (1 gram atom part) wastreated as in Example 6. The product showed predominantly a distortedperovskite-type powder pattern. Oxygen analysis confirmed the formula:Found: 15.23%; calc'd for Ba₂ RuTbO₆ : 15.22%.

EXAMPLE 8 Preparation of Ba₂ BiRuO₆

A well ground mixture of 3.387 g of BaO₂ (2 mole parts), 2.33 g of Bi₂O₃ (1/2 mole part), and 1.0107 g of Ru (1 gram atom part) was heated at750° in air for 2 hr; then reground, and heated 3 days at 700°. Theproduct showed predominantly a perovskite-type pattern, a = 4.35 A withtraces of extraneous phases. Oxygen analysis confirmed the formula:Found: 14.43% O; calc'd for Ba₂ BiRuO₆ : 14.10% O.

EXAMPLE 9 Preparation of Ba₂ YRuO₆

A well ground mixture of 3.064 g of BaO₂ (2 mole parts), 1.0215 g of Y₂O₃ (1/2 mole part), and 0.9144 g of Ru (1 gram atom part) was heated at1000° for 24 hr; reground, and heated at 1250° for 24 hr.

The product showed a distorted perovskite-type pattern indexable withthe hexagonal cell. The dimensions were refined to a = 5.890 ± 0.001 A;c = 14.495 ± 0.007 A. Oxygen analysis confirmed the formula: Found:17.42% O; calc'd for Ba₂ YRuO₆ : 17.13% O. The powder pattern is shownin Table 3. Weak extraneous peaks were ignored.

                  Table 3                                                         ______________________________________                                        Powder Pattern of Ba.sub.2 YRuO.sub.6                                         Intensity h       k       l     d.sub.obs                                                                              d.sub.calc                           ______________________________________                                        2         1       0       1     4.815    4.812                                          0       0       3              4.832                                1         1       0       2     4.171    4.171                                6         1       0       3     3.509    3.508                                100       1       1       0     2.947    2.945                                          1       0       4              2.954                                3         1       0       5     2.521    2.520                                          1       1       3              2.515                                          2       0       1              2.512                                4         2       0       2     2.407    2.406                                5         2       0       3     2.254    2.556                                24        2       0       4     2.085    2.086                                4         2       0       5     1.915    1.915                                          1       0       7              1.918                                          2       1       1              1.911                                1         2       1       2     1.863    1.863                                          1       1       6              1.868                                2         2       1       3     1.790    1.791                                23        3       0       0     1.700    1.700                                          2       1       4              1.702                                3         2       1       5     1.605    1.605                                          3       0       3              1.604                                          2       0       7              1.607                                ______________________________________                                    

EXAMPLE 10 Preparation of Sr₂ LaRuO₆

A well ground mixture in the stoichiometric ratio 2SRCO₃, 1/2 La₂ O₃ andRu was heated in air at 1000° for 1/2 hr, reground, and reheated at1100° for 24 hr. The product showed a perovskite-type powder patternwhich was more distorted than that shown in Example 2 and was notreadily indexed.

EXAMPLE 11 Preparation of Sr₂ NdRuO₆

A reaction similar to that in Example 10 was carried out except that Nd₂O₃ was used in place of La₂ O₃. This produced a material which gave adistorted perovskite-type powder pattern similar to that in Example 10.

EXAMPLE 12 Preparation of Sr₂ HoRuO₆

Sr₂ HoRuO₆ was prepared by a reaction similar to that used in Example 10except that Ho₂ O₃ was used in place of La₂ O₃. The powder patternshowed a distorted perovskite-type cell similar to that in Example 2.

EXAMPLE 13 Preparation of Sr₂ YbRuO₆

A well ground mixture of 5.9712 g of SrCO₃ (2 mole parts), 3.9848 g ofYb₂ O₃ (1/2 mole part), and 2.044 g of Ru (1 gram atom part) was treatedas in Example 14. The product showed a distorted perovskite-type powderpattern. Oxygen analysis confirmed the formula: Found: 17.99% O; calc'd:17.60%.

EXAMPLE 14 Preparation of Sr₂ YRuO₆

A well ground mixture of 2.8992 g of SrCO₃ (2 mole parts), 1.1036 g ofY₂ O₃ (1/2 mole part), and 0.9924 g of Ru (1 gram atom part) was heatedin air at 1000° for 24 hr, reground, and heated at 1150° for 48 hr,reground, and heated at 1250° for 24 hr. The X-ray powder pattern showeda distorted perovskite-type cell. Oxygen analysis confirmed the formula:Found: 20.19% O; calc'd for Sr₂ YbRuO₆ : 20.81%.

EXAMPLE 15 Preparation of Ba₂ LaRuO₆

A well ground mixture of 2.4528 g of BaCO₃ (2 mole parts), 1.7192 g ofLa₂ (C₂ O₄)₃ 4.21 H₂ O (1/2 mole part) and 0.6181 g of ruthenium powder(1 gram atom part) were ground together and heated at 1100° for 1 hour,then reground, and reheated at 1100° for 24 hours. The X-ray powderpattern showed a perovskite-type powder pattern with a few extra peaks.Chemical analysis for O, found: 15.16%; calc'd: 15.72%. The product wasreground and heated for 2 days at 1100°. The X-ray powder pattern showeda nearly single phase perovskite pattern. Chemical analysis, found:15.73% O; calc'd: 15.72% O.

EXAMPLE 16 Preparation of Ba₂ YbRuO₆

A well ground mixture of 2 mole parts of BaCO₃, 1/2 mole part of Yb₂ O₃and 1 gram atom part of Ru powder was heated as in Example 4. Theproduct showed a distorted perovskite-type pattern. It was reground andheated at 1100° for 24-48 hours. The X-ray powder pattern showed anearly single phase perovskite-type pattern with refined cellparameters, a = 5.859 ± 0.012 A, c = 14.56 ± 0.04 A. Chemical analysisfor O, found: 14.14%; calc'd: 14.89%. The low value found may indicatenonstoichiometry due to the tendency for Yb to be divalent. O contentcalculated for Ba₂ RuYb⁺² O₅.5 = 13.82%. Thus, the composition may liebetween the limits.

I claim:
 1. The metal oxides which contain pentavalent ruthenium, exhibit perovskite-type crystal structure, and are of the formula

    Q.sub.2 MRuO.sub.6

in which Q is barium or strontium, and M is yttrium, bismuth or rare earth metal of atomic number 57 to 70, provided that when Q is strontium, M is not bismuth.
 2. The metal oxides of claim 1 of the formula

    Ba.sub.2 M'RuO.sub.6

in which M' is yttrium, bismuth or rare earth metal of atomic number 57 to
 70. 3. The metal oxide of claim 2 of the formula

    Ba.sub.2 LaRuO.sub.6.


4. The metal oxide of claim 2 of the formula

    Ba.sub.2 EuRuO.sub.6.


5. The metal oxides of claim 1 of the formula

    Sr.sub.2 M"RuO.sub.6

in which M" is yttrium or rare earth metal of atomic number 57 to
 70. 